Applications from the field of indoor localization include indoor navigation, location tagging and tracking. Related art in this area has focused on passive localization, in which the localized entity does not make an active effort to get localized. For example, a camera-based person localization may not have been initiated by the person in question. Certain related art systems may not preserve user privacy, while other related art systems may preserve privacy (e.g. wireless based systems) but may not provide sufficient precision for indoor localization.
Related art systems attempt to address the problem of indoor localization by using different technologies. Related art wireless-based systems report a median localization error of more than a meter, and may involve extensive setup and tuning. The localization error for related art systems based on Global Systems for Mobile communications (GSM) and Radio Frequency Identification (RFID) also fall within a range of more than a meter. To attain sub-meter accuracy, related art optical and acoustic based systems have been developed.
Related art localization systems can conceptually be classified into source localization systems and receiver localization systems. Related art source localization systems employ multiple receivers with known positions to sense signals from a source. By analyzing these signals, the system can localize the source. Related art camera-based (optical) systems and most acoustic systems using microphones in the related art fall in this category. However, since such related art systems deploy multiple receivers, the related art systems can potentially record the user's actions or voice without an explicit approval from the user, thus raising privacy concerns.
Related art receiver localization systems can be further sub-categorized as those using unmodulated signals and those that use modulated signals. The receiver records the sensed signal and either analyzes it in-situ or sends the recorded signal to a server to process it and determine user location. Systems using unmodulated signals either use multiple receivers or use collaborative sensing while simultaneously trying to localize multiple receivers. The unmodulated systems are similar to source localization systems in that regard. Source localization systems compare signals received at receivers whose locations are known, with the signal received at the receiver whose position needs to be determined. Related art systems that use collaborative sensing of unmodulated signals require a number of receivers that are simultaneously trying to localize themselves. Other collaborative related art systems take a hybrid approach by using both a source and receiver in the device trying to localize itself. However, such collaborative systems cannot be used to localize a single receiver unless recorded signals from other receivers are available.
Related art systems using modulated signals utilize ultrasonic waves due to their better ranging accuracy as compared to those that use an audible sound. However, these systems have several limitations as they often require heavy and often expensive infrastructure by utilizing ultrasound transducers that only exist in the environment for that purpose. Further, ultrasound has a limited range as it suffers from greater attenuation while propagating through air, in comparison to an audible sound.
Additionally, ultrasonic receptors are not commonly found in mobile devices. Hence, a mobile device cannot be used for localization without requiring additional ultrasonic hardware.